The present technology relates to operation of memory devices.
Semiconductor memory is commonly used in various electronic devices. For example, non-volatile semiconductor memory is used in personal navigation devices, cellular telephones, digital cameras, laptops and other devices. For example, one type of memory uses a floating gate to store charges which represent a data state. Floating gate memory cells can be arranged in a two-dimensional structure in which NAND strings are formed on a substrate. Another type of memory uses a charge-trapping material to store charges. The charge-trapping material can be arranged vertically in a three-dimensional (3D) stacked memory structure, or horizontally in a two-dimensional (2D) memory structure. One example of a 3D memory structure is the Bit Cost Scalable (BiCS) architecture which comprises a stack of alternating conductive and dielectric layers. A memory hole is formed in the stack and a NAND string is then formed by filling the memory hole with materials including a charge-trapping layer. A straight NAND string extends in one memory hole, while a pipe- or U-shaped NAND string (P-BiCS) includes a pair of vertical columns of memory cells which extend in two memory holes and which are joined by a bottom back gate. Control gates of the memory cells are provided by the conductive layers.
However, various challenges are presented in operating such memory devices.